Evaporator system



May 28, 1968 w. E. RUSHTON EVAPORATOR SYSTEM Filed Feb.- 14, 1966 AFODQOmm .VNI

INVENTOR WILLIAM E. RUSHTON www@ ATTORNEYS United States Patent O 3,385,343 EVAPORATOR SYSTEM William E. Rushton, South Holland, lll., assignor to Whiting Corporation, a corporation of Illinois Filed Feb. 14, 1966, Ser. No. 527,182 11 Claims. (Cl. 159-26) The present invention generally relates to improved apparatus and method for concentrating phosphoric acid. More particularly, this invention is concerned with certain improvements and innovations in forced circulation evaporators which are used for concentrating Wet process phosphoric acidi. In this application phosphoric acid strength will be identified by referring to the equivalent P205 concentration since this is the accepted -acid strength identifying designation used by wet process phosphoric acid industry.

In the manufacture of phosphoric acid by the wet process method, phosphate rock is reacted with sulphuric acid to produce a phosphoric acid product having a P205 concentration of about by weight. Various types of evaporators have been used for concentrating this phosphoric acid product. The present invention is directed to an improved forced circulation evaporator construction which offers significant advantages over these prior art evaporators. In order to more fully present these advantages, a brief explanation of the prior artis appropriate.

Horizontal-tube cast lead evaporators were Iamong the iirst types of vacuum evaporation equipment that were used for concentrating wet process phosphoric acid. These evaporators are operated on a continuous batch basis with the dilute phosphoric acid being fed to the evaporator continuously and evaporated until the entire contents of the evaporator are at the desired concentration. The contents of the evaporator are then discharged and the evaporator boiled out. These evaporators have relatively short operating cycles (operating periods between boilouts), generally running from about one to two days depending upon the nature of the acid feed and the concentration of the product. Another disadvantage of this particular type lof evaporator is that the initial phase of the boilout usually requires ushing of the heat exchanger surfaces with -a high velocity water stream, such as with a fire hose, to break the scale loose.

Another type of evaporator used in wet process phosphoric acid concentration operations is the natural circulation long-tube vertical evaporator. These evaporators have the advantage of offering continuous operation with longer operating cycles between boilouts (generally from three to seven days) over those obtainable with the horizontal tube evaporator systems. The general problem with this type of evaporator, however, is that when the tubes become plugged, the scale therein is very difiicult to remove. In fact, when karbate heat exchanger tubes are used, almost any type of mechanical tube cleaning will result in at least some of the tubes being broken.

Forced circulation evaporators have also been employed for concentrating phosphoric acid. In these systems, the evaporating chamber has a discharge leg which communicates with a circulating pump which in turn communicates with a vertically aligned heat exchanger wherein the recycle stream is heated prior to being lreturned to the evaporating chamber. One of the problems associated with this type of evaporator is caused by scale accumulating on the interior walls of the evaporating chamber and breaking loose. Chunks of this scale follow the circulating acid to the heat exchanger causing the heat exchanger tubes to plug up with stagnant pools of acid entrapped herein. Additional scale settles out from these stagnant pools of acid causing the tubes to plug even further.

In a first effort to overcome the scaling problem, lump screens were installed on the tube inlet side of the heat ice exchanger. These screens were designed to prevent large pieces of scale from getting into the tubes and were shaped so that as these solids contacted the screen they would constantly recirculate within the liquor chamber until they were sufficiently reduced in size so that they would pass through the screen. Such screens did not provide a complete answer to the problem since they would plug up themselves and took several hours for removal, cleaning and installation during evaporator shutdown.

Another unfavorable aspect of using conventional forced circulation evaporators for phosphoric -acid concentration is that the circulating pumps therein require the provision of a stuing box. With a properly packed stuffing box around 250 to 500 pounds of water per hour will be introduced into the recycle liquor. With an improperly packed or worn stuffing box, 1000 pounds per hour of water or more can contaminate the recycle stream. Accordingly, this source of water in the recycling phosphoric lacid liquor adversely effects the over-all efficiency and puts an additional load on the evaporator.

The present invention is directed to a forced circulation evaporator construction which has a number of significant innovations which overcome the above-mentioned problems characteristic of prior art equipment.

In accordance with the present invention, the full flow of recycle liquid from the evaporating chamber is discharged intoa large capacity circulating tank which provides increased retention time for the acid in the system. This increased retention time acts, in part, to provide the evaporator of the present invention with a substantially increased operating cycle between boilouts.

The problems caused by stufiing boxes in the prior art evaporators are eliminated since the circulating tank of the present invention operates at atmospheric pressure enabling the use of a vertical axial flow pump located in the circulating tank. In this regard, it is important to note that in addition to the above-mentioned water contamination problem which can be significant in the case of worn or improperly packed stuffing boxes, maintenance is substantially reduced since vertical pumps of the type used in the present invention do not require packing. Conventional circulating pumps on prior art forced circulation evaporators require repacking every two t-o six weeks.

The integral circulating tank of the present invention offers another advantage which is particularly important in multi-stage evaporator operations. By arranging the integral circulating tanks so that the product discharge of one will feed by gravity to the feed inlet of the next stage, it is possible to completely eliminate the need for transfer pumps. This not only reduces installation cost for the evaporator system but also eliminates a source of potential breakdown therein.

Tube plugging problems encountered with prior art evaporators are so effectively overcome with the present invention that, if desired, horizontal heat exchangers can be used in place of vertical heat exchangers thereby reducing the over-all height of the evaporating unit.

In a modification of the forced circulation evaporator system of the present invention, an auxiliary boilout system is provided which boilout system cooperates with the other components in the evaporator system thereof to facilitate the tube cleaning and effectively reduce the time required for each tube cleaning operation.

It is therefore an object of the present invention to provide an improved forced circulation evaporator apparatus and method which is particularly suitable for concentrating a phosphoric acid feed to produce a concentrated phosphoric acid product.

Another object of the present invention is to provide an improved forced circulation apparatus and method for concentrating phosphoric acid which enable increased operation time between shutdowns due to the elimination of tube pluggage caused by the transmission of large chunks of scale or other solids to the heat exchanger.

Another object of the present invention is to provide an improved multi-stage forced circulation evaporator construction which eliminates the need for transfer pumps between the respective stages of the evaporator.

Another object of the present invention is to provide an improved forced circulation apparatus and method which incorporates an auxiliary boilout system that cooperates with the other components in the evaporator system, to facilitate tube cleaning and substantially reduce the time therefor.

Another object of the present invention is to provide an improved forced circulation evaporator apparatus for concentrating phosphoric acid which apparatus includes a large capacity circulating tank arranged to receive the full flow of recycle liquor` from the evaporating chamber and which acts to substantially increase the acid retention time in the evaporator.

Another object of the present invention is to provide an improved forced circulation evaporator which includes a large capacity circulating tank arranged to receive the full iiow of recycle liquor from the evaporating chamber, which circulating tank is equipped for removing scale and other solid contaminants from said liquor prior to transmission of said recycle liquor to the heat exchanger.

Another object of the present invention is to provide an improved forced circulation evaporator adapted for concentrating phosphoric acid which evaporator is characterized by effective scale removal components enabling the use of horizontal heat exchangers in place of vertical heat exchangers.

Another object of the present invention is to provide an improved forced circulation evaporator wherein the pumping means does not require a stuffing box.

Other objects and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment of the present invention taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a partially schematic flow diagram of a forced circulation evaporator system embodying principles of the present invention; and

FIGURE 2 is a horizontal plan view of the circulating tank shown in FIGURE 1.

Referring to the drawing, and with particular reference to FIGURE l, the numeral 11 generally designates a forced circulation evaporator system embodying principles of the present invention. As is shown, evaporator system 11 generally includes an evaporating chamber 12, a circulating tank 13 and heat exchanger 14.

Evaporating chamber 12 has an overhead vapor outlet indicated by the numeral 16. Vapors exiting through outlet 16 are directed into a condenser (not shown) which is fed with water or other coolant. Evaporating chamber 12 includes a frusto-conical bottom 17 which terminates in a iianged connection 18 sized to be iixedly mounted to a mating tiange 19 on vertical leg or discharge nozzle section 20. As is shown, section 20 is also equipped with a frusto-conical top section 20a which generally corresponds to frusto-conical section 17 of the evaporating chamber 12. Liquid discharge nozzle 20 is preferably sized to discharge adjacent the bottom of circulating tank 13 and in accordance with an important aspect of the present invention, discharges all of the recycle liquor from the evaporator into circulating tank 13 rather than pust a portion thereof. Since evaporator 12 is operated under vacuum conditions (generally at an absolute pressure of two to eight inches of mercury), a liquid level 21 is maintained therein.

In the illustrated embodiment, phosphoric acid to be concentrated is fed into the circulating tank at feed inlet 22. Product discharge outlet 23 discharges the product from circulating tank to storage or other evaporating equipment for further processing. An overliow Weir 24 controls the flow of liquid in circulating tank 13 through product discharge outlet 23. In this connection, it should be noted that for illustrative purposes evaporator system 11 is shown as a single stage operation. It will, however, be apparent to those skilled in this art that the principles of the present invention are equally applicable to multistage evaporator systems. In multi-stage evaporator systems, the product discharge from the first stage will constitute the feed to the second stage, and the product discharge from the second stage will constitute the feed to the third stage.

An important advantage of the integral circulating tank 13 of the present invention is that it eliminates the need for transfer pumps between evaporator stages in multistage evaporator systems. The elimination of pumps in any evaporator system is always important since these components not only add to the installation cost but also represent a place of potential breakdown. With the present invention, transfer pumps are eliminated by arranging the circulating tanks for each of the stages so that the product discharge from the preceding stage will flow by gravity to the feed inlet for the next stage. For example, if evaporator 11 were the first stage, product discharge line 23 would be positioned at a higher elevation than the liquor level in the circulating tank for the second stage.

While in the illustrated embodiment, feed inlet 22 is specifically located in the circulating tank 13, it will be apparent to those skilled in this art that the inlet might be placed at other suitable locations. From the standpoint of reducing the likelihood of having the product mix with the incoming feed, it is preferred that feed inlet 22 be located remote from the product outlet 23. A baie plate 25, partially extending across the circulating tank 13 (see FIGURE 2) serves to divide the tank 13 into two communicating sections. Phosphoric acid in the circulating tank 13 follows a counterclockwise iiow path, enabling the product to be withdrawn at line 23 prior to its being diluted with incoming feed from inlet 22.

As is illustrated, the phosphoric acid contained in the circulating tank is transmitted to the heat exchanger 14 through a conduit 26 which is of large diameter, making the provision of valves therein costly and impractical. In this connection, it should be noted that in the illustrated preferred embodiment of the present invention valve means for controlling the flow between circulating tank 13 and heat exchanger 14 is provided by seal loop 26u which will be more fully described below. However, it will at the same time be apparent that in modifications of apparatus embodying the present invention other flow control means such as, for example, a valve, could be employed. Conduit 26 has an open end or inlet 27 in the circulating tank which is equipped with a vertical axial liow pump 28 for providing forced circulation through the evaporator system.

Axial flow pump 28 includes a motor (not illustrated) and bearing housing 29 mounted above the circulating tank 13 as shown in FIGURE l. Bearing housing 29 is connected to a screw-type propeller 30 by means of a vertically extending shaft 31. As is shown, pump 28 does not require a stuiiing box since circulating tank 13 operates at atmospheric pressure. Accordingly, the evaporator construction of the present invention offers the advantage of forced circulation without the maintenance problems of conventional forced circulation evaporators. Furthermore, problems caused by poor packing of a stuffing box (i.e. having up to 1000 pounds of water per hour contaminating the recycle stream and thereby increasing the evaporation load) are completely eliminated.

Circulating tank 13 has a large capacity, generally at least equal to the total volume of the remaining process system (i.e. heat exchanger, evaporator and connecting process lines) and is preferably two or three times this size. Accordingly, the liquid velocity therein is relatively low, enabling large pieces of scale and other solids which fall into the tank to settle to the bottom. A circular lump screen 32 tixedly secured to support stand 32a is provided ground the inlet'27 of process line 26 in order to prevent other solids, of undesirable size, from reaching heat exchanger 14. Screen 32 has a greatly enlarged surface over that of prior art lump screens both by reason of its circular configuration and because its size is not limited to the diameter of process line 26. Plugging of screen 32 is virtualy eliminated by reason of the very large surface area thereof and the low liquid velocity in the tank. Solids'which collect on the floor 33 of circulating tank 13 can be removed manually or, if desired, a raking mechanism or other appropriate oor sweeping device can be employed to provide continuous solids removal during evaporator operation. Accordingly, it should be noted that the circulating tank and circular lump screen of the present invention not only effectively prevents the transmission of undesirably sized solids to the heat exchanger, but also provide removal of these solids from the system without necessitating evaporator shutdown.

The liquid contained in the integral circulating tank 13 is transmitted through process line 26 into the tube inlet side 34 of heat exchanger 14. If desired, conduit 26 can be equipped with a suitable expansion joint 36. The liquid acid transmitted into the tube inlet side passes through the heat exchanger tubes, generally designated by the reference numeral 37, and upon being heated, exits therefrom through tube outlet 38 which is connected to a large diameter process line 39 that returns the heated acid to the interior of the evaporator chamber 12. The hydrostatic head created by the volume of liquid in the vertical portion 39a of process line 39 prevents boiling in the heat exchanger. Thus, when the liquid phosphoric acid is transmitted into the evaporating chamber which is under vacuum, it will immediately ash with the vapor product exiting at 16.`As was true with process line 26, theiprovision of valves or blocking plates in process line 39 is impractical by reason of the large diameter thereof and also because their operation is hampered by the build up of precipitates such as CaSO4 and various metal fluosilicates which are present in the system.

In the preferred embodiment of the present invention illustrated in FIGURE 1, a boilout system is provided. This boilout system greatly facilitates the tube cleaning operation in that it permits recycling of a boilout solution through the heat exchanger tubes'without having to circulate a large volume of boilout solution through the entire process side of the evaporator system. In this connection, it is important to note that the boilout system described herein is not essential to the other aspects of the present invention.l For example, the integral circulating tank 13 offers advantages apart from those which it provides in cooperative combination with the boilout system.

The boilout system of this invention includes a boilout tank 40 which communicates with the evaporator system by means of a discharge vline 41 that feeds into process line 39 and a return line 42 which interconnects the boilout tank with the process line 26. A suitable circulating pump 43 is provided in discharge line 41 for providing forced circulation of the boilout solution. Valves 44 and 46 are provided in lines 41 and 42, respectively, so that the boilout system can be disconnected from the evaporator during operation of the evaporator when phosphoric acid is being concentrated. In the illustrated embodiment, the ow of boilout solution is the reverse of the normal acid ow, thereby facilitating cleaning 'of tubes which plug up at the phosphoric acid inlet side (adjacent tube inlet 34).

Suitable boilout solutions for use in phosphoric acid evaporators include aqueous solutions of H2804 and 5% to 7% aqueous solutions of HZSiF. As noted previously, both process lines 26 and 39 are of a large diameter making the provision of valves therein for closing off the heat exchanger from the other components in the evaporator system impractical. At the same time, it is highly desirable to provide flow control means for sealing off the heat exchanger from the rest of the system so that there will not be any mixing of the boilout solution with the phosphoric acid. To accomplish this sealing olf of the heat exchanger 14 from the other components i-n the illustrated embodiment of the evaporator system, the boilout system of the present invention is arranged so that its highest point of elevation is below the process line 39 `and -below the seal loop portion 26a of process line 26. Accordingly, seal loop 26a acts as a. valve between circulating tank 13 and heat exchanger 14, enabling t-he boilout solution to be pumped through the heat exchanger without ymixing with the phosphoric acid stored in the circulating tank. Loop 26a is sized so that its height is greater than the head loss through the heat exchanger. It will, of course, be appreciated that in other modifications of this evaporator systern la valve could be provided in conduit 26 enabling boilout tank to be located .at any elevation. In this regard, if the level of boilout solution in tank 40 were at a higher elevation than process conduit 39, it would also be necessary to equip process line 39 with a suitable flow control means in order to have ow of the boilout solution through the heat exchanger 14 only (i.e. to in effect seal olf the heat exchanger from the evaporating chamber 12 and circulating tank 13).

When tube cleaning is to be done, the vacuum in the evaporating chamber is broken causing the acid therein to drain into the circulating tank 13. After the contents of the evaporating chamber 12 have Idrained into the circulating tank 13, the acid contained in the heater is transferred into the circulating tank. In systems wherein the Siphon action developed in the process line 26 is not suicient to drain the heat exchanger, a heater drain pump 65 can be provided for transmitting this acid to the circulating tank.

After the evaporating chamber 12 and heat exchanger I14 are completely drained, valves 44 and 46 are opened :and the circulating pump 43 activated causing the boilout solution to liow through line 47 into the tube outlet side 38 of heat exchanger 14 through the tubes (in a path which is reverse to the acid ow) `and exit out the tube inlet side '34, returning to the boilout tank 40 through boilout return line 42.

While the above description of a preferred embodiment of the present invention is directed to a phosphoric :acid evaporator system, it should be noted that the principles of this invention have applicability to forced circulation evaporator systems generally. In particular, many of the unique advantages obtained by use of the integral circulating tank and boilout circuit described above can be `advantageously employed in forced circulation evaporator systems adapted for concentrating other materials.

"One of the significant advantages of the present invention is the unique boilout technique thereof. In conducting :a tube cleaning or boilout in a conventional forced circulation evaporator it is necessary to lirst completely drain the entire evaporating system (Le. evaporating chamber and process side of heat exchanger) and transfer the slurry contained therein to a separate storage area. This, of course, then necessitates the allocation of an extensive area for storage purposes during the boilout. Such allocation is not necessary with evaporator apparatus of the present invention.

After all the slurry has been drained and transferred to a separate storage area, the heat exhcanger tubes are then checked for plugging. If any of the tubes are plugged, the plugs are removed. The evaporator is then refilled with boilout solution to a level which is above that of the normal operating level. Accordingly, with conventional forced circulation evaporators, it is necessary to employ a volume of boilout solution which is even greater than the volume of slurry Iremoved from the system. The amount of boilout solution required for a typical boilout in apparatus of the present invention is substantially less. In particular, the quantity of boilout solution required with apparatus embodying the novel boilout circuit of this invention, is that which is suliicient to provide circulation through the process side of the heat exchanger only.

In the conventional forced circulation evaporators, after the boilout solution has been circulated through the entire evaporator system to accomplish the desired degree of scale removal, it is necessary that the boilout solution be drained from the evaporator system and transferred to a suitable disposal or storage area. In evaporator systems embodying the principles of the present invention, the boilout system is merely transferred to the existing boilout tank which is already coupled to the evaporator system for ease and facility in this particular phase of operation.

Significantly, it should be noted that the time required for boilout in apparatus of the present invention is substantially reduced since boilout is conned to those lareas wherein scale buildup is most critical. Furthermore, that the integral circulating tank 13 of the present invention enables the removal lof a substantial portion of scale (that which has settled in the circulating tank) during operation of the evaporator when the slurry is being concentrated.

The restarting of an evaporator after boilout is complete is also greatly facilitated by the present invention since the evaporator is already charged with slurry at the design discharge concentration. Accordingly, it is only necessary with the present invention to pull .a vacuum on the system, start up the feed and send steam, or other heating medium, through the heat exchanger 14. Of course, with the conventional equipment, the drained acid must be recharged with the slurry previously removed therefrom.

In the foregoing specification a detailed description of a preferred embodiment of the present invention has been set forth for purposes of explanation. It will be apparent, however, that modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the present invention.

I claim:

1. An improved forced circulation evaporator system comprising an evaporating chamber, a circulating tank, and a heat exchanger, said evaporating chamber being elevated above said circulating tank and communicating with said circulating tank through an upright liquor discharge leg arranged for discharge of the entire recycle liquor flow from said evaporating chamber into said circulating tank, vacuum means communicating with said evaporating chamber, said circulating tank communicating with the atmosphere for normally operating saidcirculating tank at atmospheric pressure simultaneously while said evaporating chamber is operating under vacuum, means for selectively venting said evaporating chamber to break the vacuum maintained therein and thereby immediate-ly discharge the liquor contents of said evaporating chamber into said atmospheric circulating tank, said circulating tank being sized to contain the total volume of all liquor present in said evaporator system during normal operation below a predetermined maximum liquor level in said tank, a first process pipe communieating said circulating tank with the process inlet side of said heat exchanger, a second process pipe interconnecting the process outlet side of said heat exchanger with said evaporating chamber, the inlet of said first process pipe being located within said circulating tank, a pump operatively disposed with respect to said first process pipe inlet for effecting forced circulation of the liquor in said evaporator system, and means for preventing the transmission of solid particles of undesirable size into the inlet of said first process pipe, the impeller of said pump being located below the normal operating liquor level in said circulating tank and being operatively connected to a drive means, said drive means being mounted above said predetermined maximum liquor level in said circulating tank whereby said pump and drive means can be operated without the provision of a stuffing box therebetween.

2. The improved forced circulation evaporator of claim 1 wherein a portion of said first process pipe extends above the maximum liquor level in said circulating tank and said second process pipe communicates with said evaporating chamber at an elevation above the maximum elevation of said first process pipe.

3. The improved forced circulation evaporator system of claim 1 which is equipped with a boilout circuit comprising a boilout solution storage tank and means for selectively communicating the boilout solution storage tank with the evaporator system for effecting flow of said boilout solution through the process side of said heat exchanger, at least a portion of each of said first and second process pipes having an elevation above the maximum liquor level in said boilout circuit whereby when said boilout solution is circulating through the process side of said heat exchanger said boilout solution will be confined to the process side of said heat exchanger only.

4. The improved forced circulation evaporator system of claim 1 wherein said first process pipe is provided with a seal loop, the bight portion of said seal loop extending above both said heat exchanger and said predetermined maximum liquor level in said circulating tank.

5. The improved forced ci-rculation evaporator system of claim 1 wherein said means for preventing the transmission of solids of undesirable size into the inlet of said first process pipe comprises a particle entrapment screen located within said circulating tank.

6. The improved forced circulation evaporator system of claim 5 wherein said particle entrapment screen comprises a circular vertically extending screen positioned around the inlet of said first process pipe in said circulating tank.

7. An improved forced circulation evaporator system particularly adapted for concentrating wet process phosphoric acid feed, said evaporator system comprising a heat exchanger, an evaporating chamber, and a circulating tank, said evaporating chamber being elevated above said circulating tank and communicating with said circulating tank through an upright liquor discharge leg arranged for discharge of the entire recycle liquor flow from said evaporating chamber into said circulating tank, vacuum means communicating with said evaporating chamber, said circulating tank communicating with the atmosphere for normally operating said circulating tank at atmospheric pressure simultaneously while said evaporating chamber is operating under vacuum, means for selectively venting said evaporating chamber to the atmosphere whereby the entire liquor contents in said evaporating chamber will be immediately discharge into said circulating tank, a first process pipe interconnecting the circulating tank with the process inlet side of said heat exchanger, the inlet of said first process pipe being located within said circulating tank, a pump operatively disposed with respect to the inlet of said first process pipe for providing forced circulation of the liquor in said circulating tank into said first process pipe, a second process pipe interconnecting the process outlet side of said heat exchanger with the inlet of said evaporating chamber, means for preventing the transmission of solid particles of undesirable size into the inlet of said first process pipe, the impeller of said pump being located below thel normal operating liquor level in said circulating tank and being operatively connected to a drive means, said circulating tank being sized to contain the total volume of all liquor present in said evaporator system during normal operation thereof at a predetermined maximum liquor level, said drive means being mounted above said predetermined maximum liquor level in said circulating tank, whereby said pump and drive means can be operated Without the provision of a stuffing box therebetween.

8. The improved forced circulation evaporator system of claim 7 wherein a portion of said rst process pipe extends above the maximum liquor level in said circulating tank and said second process pipe connects with said evaporating chamber at an elevation above the maximum elevation of said first process pipe.

9. The improved forced circulation evaporator system of claim 7 Whe-rein said rst process pipe is provided with a seal loop, the bight portion of said seal loop extending above both lsaid heat exchanger and said predetermined maximum liquor level in said circulating tank.

10. The improved forced circulation evaporator system of claim 7 wherein said means for preventing the transmission of solids of undesirable size into the inlet of said rst process pipe comprises a particle entrapment screen located within said circulating tank.

11. The improved forced circulation evaporator of References Cited UNITED STATES PATENTS 1,006,823 10/1911` Block 159-2 1,831,121 11/1931 Kermer l59-27 X 1,840,234 l/1932 Hughes 15S-26 X 1,953,346 4/1934 Gard et al. 195-74 2,176,152 10/1939 Sadtler 159--26 2,781,089 2/1957 Mair et al 159-20 FOREIGN PATENTS 16,738 1899 Great Britain.

NORMAN YUDKOFF, Primary Examiner'.

I. SGFER, Assistant Examinez'. 

1. AN IMPROVED FORCED CIRCULATION EVAPORATOR SYSTEM COMPRISING AN EVAPORATING CHAMBER, A CIRCULATING TANK, AND A HEAT EXCHANGER, SAID EVAPORATING CHAMBER BEING EVELATED ABOVE SAID CIRCULATING TANK AND COMMUNICATING WITH SAID CIRCULATING TANK THROUGH AN UPRIGHT LIQUOR DISCHARGE LEG ARRANGED FOR DISCHARGE OF THE ENTIRE RECYCLE LIQUOR FLOW FROM SAID EVAPORATING CHAMBER INTO SAID CIRCULATING TANK, VACUUM MEANS COMMUNICATING WITH SAID EVAPORATING CHAMBER, SAID CIRCULATING TANK COMMUNICATING WITH THE ATMOSPHERE FOR NORMALLY OPERATING SAIDCIRCULATING TANK AT ATMOSPHERIC PRESSURE SIMULTANEOUSLY WHILE SAID EVAPORATING CHAMBER IS OPERATING UNDER VACUUM, MEANS FOR SELECTIVELY VENTING SAID EVAPORATING CHAMBER TO BREAK THE VACUUM MAINTAINED THEREIN AND THEREBY IMMEDIATELY DISCHARGE THE LIQUOR CONTENTS OF SAID EVAPORATING CHAMBER INTO SAID ATMOSPHERIC CIRCULATING TANK, SAID CIRCULATING TANK BEING SIZED TO CONTAIN THE TOTAL VOLUME OF ALL LIQUOR PRESENT IN SAID EVAPORATOR SYSTEM DURING NORMAL OPERATION BELOW A PREDETERMINED MAXIMUM LIQUOR LEVEL IN SAID TANK, A FIRST PROCESS PIPE COMMUNICATING SAID CIRCULATING TANK WITH THE PROCESS INLET SIDE OF SAID HEAT EXCHANGER, A SECOND PROCESS PIPE INTERCONNECTING THE PROCESS OUTLET SIDE OF SAID HEAT EXCHANGER WITH SAID EVAPORATING CHAMBER, THE INLET OF SAID FIRST PROCESS PIPE BEING LOCATED WITHIN SAID CIRCULATING TANK, A PUMP OPERATIVELY DISPOSED WITH RESPECT TO SAID FIRST PROCESS PIPE INLET FOR EFFECTING FORCED CIRCULATION OF THE LIQUOR IN SAID EVAPORATOR SYSTEM, AND MEANS FOR PREVENTING THE TRANSMISSION OF SOLID PARTICLES OF UNDESIRABLE SIZE INTO THE INLET OF SAID FIRST PROCESS PIPE, THE IMPELLER OF SAID PUMP BEING LOCATED BELOW THE NORMAL OPERATING LIQUOR LEVEL IN SAID CIRCULATING TANK AND BEING OPERATIVELY CONNECTED TO A DRIVE MEANS, SAID DRIVE MEANS BEING MOUNTED ABOVE SAID PREDETERMINED MAXIMUM LIQUOR LEVEL IN SAID CIRCULATING TANK WHEREBY SAID PUMP AND DRIVE MEANS CAN BE OPERATED WITHOUT THE PROVISION OF A STUFFING BOX THEREBETWEEN. 